Mechanism-free ornithopters, also referred to as solid-state ornithopters, based on piezoelectric actuators do not need electromagnetic motors or conventional mechanisms, potentially saving weight and energy consumption, and reducing mechanical complexity. In such vehicles, the aim is to achieve lift and thrust purely by surface-mounted piezoelectric actuators; however, the generating sufficient lift and thrust without mechanism augmentation is extremely difficult; and has not been demonstrated. The optimization of wing substrate topology, actuator placement, and excitation parameters requires a computationally efficient model of the dynamic behavior of a solid-state ornithopter. In this article, a reduced-order lumped-parameter model is proposed for ornithopters with piezocomposite flapping wings. The piezoelectric, mechanical, and fluid domains are modeled and coupled by Hamilton’s principle. Based on the Rayleigh-Ritz method, the wing motion is described by the assumed bending and twisting modes to predict plunging and pitching motions. The fluid effects considered are added mass and quasi-static aerodynamic forces. A vortex lattice code is used to obtain aerodynamic coefficients for the wing. The body-wing and the wing-fluid interactions are accounted for in the model. Gliding flapping flight simulations with initial velocity and height are conducted. Contribution of active flapping are found by comparison to flight with non-flapping compliant wings.